Remove the man directory to the subdirs to prevent building the man pages

Signed-off-by: Benoît Allard <benoit.allard@greenbone.net>

--- a/Makefile.am	2017-03-27 09:53:19.988820588 +0200
+++ b/Makefile.am	2017-03-27 09:54:14.325817466 +0200
@@ -15,7 +15,7 @@
 # You should have received a copy of the GNU General Public License
 # along with this program.  If not, see <http://www.gnu.org/licenses/>.
 
-SUBDIRS = lib src man po
+SUBDIRS = lib src po
 EXTRA_DIST = cfg.mk maint.mk \
   .prev-version THANKS-to-translators THANKStt.in \
   .version \
